Problem: $4lm - ln - 2l + 10 = -9m + 2$ Solve for $l$.
Combine constant terms on the right. $4lm - ln - 2l + {10} = -9m + {2}$ $4lm - ln - 2l = -9m - {8}$ Notice that all the terms on the left-hand side of the equation have $l$ in them. $4{l}m - 1{l}n - 2{l} = -9m - 8$ Factor out the $l$ ${l} \cdot \left( 4m - n - 2 \right) = -9m - 8$ Isolate the $l$ $l \cdot \left( {4m - n - 2} \right) = -9m - 8$ $l = \dfrac{ -9m - 8 }{ {4m - n - 2} }$ We can simplify this by multiplying the top and bottom by $-1$. $l= \dfrac{9m + 8}{-4m + n + 2}$